1. Field of Technology
The present invention relates to an image scanning apparatus having a plurality of image scanning sensors.
2. Description of Related Art
Image scanners are commonly used to scan image data printed on the surface of paper, cards, and other source media. Such image scanners emit light from an LED or other light source disposed in the scan head in the direction of the medium to be scanned while the medium being scanned is held against the scan head. An image scanning sensor disposed in the scan head then detects the light reflected back from the scanned medium to take an image of the scanned medium.
There are two basic types of image scanning sensors, flatbed and sheetfed. With a flatbed scanner, the medium to be scanned remains stationary while the scan head travels relative to the medium for taking an image of the scanned medium. With sheetfed scanners, the scan head remains stationary while the medium being scanned is both held in contact against the scan head and moved relative thereto for taking an image of the scanned medium.
Flatbed scanners are necessarily large because space sufficient for the scan head to traverse the entire surface of the scanned medium must be provided for inside the scanner. Scanner size can therefore be reduced more easily with a sheetfed type of scanner than a flatbed scanner.
FIG. 5 is a side section view of a conventional sheetfed image scanner 300. Original sheets P placed on a supply tray 302 are raised by a raising/lowering tray 303, picked up by the supply roller 304, and conveyed from the insertion slot F into the sheetfed image scanner 300. The sheet P is then transported by the separation roller pair 305 and feed roller pair 306 to the image sensor 301, and the original is imaged by the image sensor 301. When scanning is completed, the imaged sheet P is discharged by exit roller pair 307 from the exit opening R to the exit tray 308. A conventional sheet fed image scanner is disclosed, for example, in Japanese Unexamined Patent Appl. Pub. H11-284801.
A contact image sensor (“CIS”) is typically used in sheetfed scanners. CIS sensors scan the medium using a plurality of photodetectors arranged widthwise of the scanned medium through a lens called a rod lens array. Unlike optical reduction image scanners (CCD scanners), CIS image sensors do not require a mirror. Sensor size can therefore be reduced, and the overall scanner size can also be reduced.
In order to image the scanned medium with high precision in a CIS type image scanner, the scanned medium must be pressed to and conveyed over the document glass of the image scanning sensor using e.g., springs or pressure rollers and moving means such as transportation rollers under the control of a motor. In order to scan media having different thicknesses, such as checks and driver licenses, using a single image scanning sensor, the medium must be pressed to the document glass of the image scanning sensor with pressure appropriate to the thickness of the medium. The need to apply an appropriate pressure commensurate with the thickness of the medium complicates the construction of the scanning apparatus.
One way to solve this problem is to provide a plurality of different image scanning sensors with one or more selected according to the thickness of the media to be scanned. However, providing a plurality of image scanning sensors in a single device necessitates the use of a different signal processing circuit, control circuit, and other peripheral elements for each selection of a different image scanning sensor. This increases the cost and the size of the control circuit board.
The image scanning apparatus of the present invention employs a plurality of image scanning sensors in a construction which does not require a different signal processing circuit, control circuit, and other peripheral elements etc. such that the scanner cost and size is minimized.